Circular type sawblades are used for cutting cants or lumber. These circular sawblades are typically provided with a mounting hole or eye, and an arbor is positioned in this mounting hole so that the sawblade is mounted on the arbor. The arbor is also rotatably connected to a source of drive power. In this way, the operation of the power source causes rotation of the arbor which in turn causes rotation of the circular sawblade.
The circular sawblade and the arbor are operatively connected to one another so that the rotation of the latter results in rotation of the former. In known types of circular sawblades, this operative connection is typically provided by projections extending outwardly from the outer periphery of the arbor that engage recesses formed in the inner periphery of the mounting hole of the circular sawblade. The projections are usually rounded or convex male drive pieces spaced intermittently and circumferentially around the arbor periphery, although the projections can also be in the form of generally truncated cone shaped projections. The recesses in the arbor are correspondingly configured to receive the projections.
Typically, the sawblade is mounted onto the arbor endwise. The sawblade slides over the arbor until the desired operating position on the arbor is reached. Under operating conditions, the sawblade is maintained in its desired position with sawguides which prevent undesirable movement of the sawblade. This keeps the kerf or cutting width created by the blade narrow which is desirable in order not to avoid wood wastage during the sawing operation.
Arbors and sawblades which employ projections and recesses configured in the aforementioned conventional manner suffer from a variety of disadvantages and drawbacks. In one respect, the shape of the interfitting projections on the arbor and the corresponding recesses in the sawblade produces interface forces acting on the sawblade that have a radial component directed outwardly. This outwardly directed component of the interface force, which functions as an outward pushing force at the blade/arbor interface, is quite disadvantageous as it can cause a variety of problems. In one respect, the pushing force tends to enlarge or deform the mounting hole or eye in the circular sawblade over time as the sawblade is used. The deformation or expansion of the eye in the sawblade contributes to the reduction in tension in the sawblade which then requires that the sawblade be repeatedly re-tensioned.
The deformation or enlargement of the sawblade eye also leads to the loss of geometrical conformity of the sawblade to the arbor. As a result, blade centering is detrimentally affected. When the blade is not centered on the arbor, the teeth farthest away from the rotational axis of the arbor perform the greatest part of the cutting operation, that is they take the deepest cuts on the wood being cut. If this out of center condition is particularly excessive, for a given rotational speed of the sawblade and a given feed rate of the wood, some teeth may perform virtually no cutting. The out of center condition of the sawblade and the resulting difference in cutting action of the various teeth on the sawblade causes non-uniform heating of the sawblade, thus leading to undesirable distortion of the sawblade. Thus distortion is disadvantageous in that it negatively impacts the cutting efficiency of the sawblade as well as cutting deviation.
When the sawblade eye does not properly conform to the arbor, the sawblade is able to shift radially as it rotates and this causes eccentricity. As the eccentricity increases, undesirable imbalance forces are introduced and these imbalance forces impart undesirable forces to the blade. Since the imbalance force is represented by the eccentricity times the mass times the square of the rotational speed of the circular sawblade, increases in the eccentricity necessarily causes an increase in imbalance which imparts undesirable forces to the circular sawblade.
The enlargement of the eye in the sawblade that results from the pushing force at the sawblade/arbor interface in conventionally configured sawblade driven surfaces and arbor drive surfaces is also undesirable as the points of contact between the sawblade and the arbor change over time and on occasion become non-uniformly distributed. This can lead to blade flutter during cutting and a loss of stability. In addition, the radially outwardly directed component of force causes the sawblade to bend and kink during operation. This is disadvantageous at least from the standpoint of wear with respect to the sawguides. The sawguides which are positioned on opposite sides of the sawblade are designed to direct fluid at the blade from opposite sides of the blade so that the blade hydroplanes. If the sawblade is able to kink or bend on the arbor, the sawguides on either side of the circular sawblade wear more quickly and thus must be resized rather regularly.
Conventional configurations of the arbor and sawblade also present problems from the standpoint of safety, tolerances and sawblade driving efficiency. From a safety standpoint, there has arisen the unfortunate practice of "tree spiking" by those protective be felled. This practice involves driving large nails or spikes into the trunks of trees before cutting. Often the spikes are not readily observed by either the fellers or the sawmill operators with the result that during sawmill operations, the sawblade may strike a spike within the cant or log during the cutting operation. This can be quite dangerous since the sawblade can tear or fragment, whereupon pieces of shrapnel are distributed at high energy levels throughout the area where the cutting is taking place. This disintegration takes place because there is no retention of the sawblade by the spline when the sawblade splits or tears after contact with the spike.
From the standpoint of operating tolerances, the convex type engaging surfaces on the arbor result in a series of point contacts between the interfitting surfaces of the arbor and the circular sawblade. This point contact results in a series of high stress points between the arbor and the sawblade which increases wear on both members and reduces the driving efficiency between the arbor and the sawblade.
Yet a further disadvantage is that the arbor has to be hardened to a hardness greater than that of the sawblade. This practice is time consuming and expensive.
One type of sawblade and arbor system used for cutting wood involves what is referred to as a collared sawblade. In these types of systems, the sawblades are mounted on sawblade collars (virtually steel plates) which in turn are mounted on the arbor. U.S. Pat. No. 3,703,915 discloses such a system. This patent describes a thin kerf saw machinery that includes an arbor, and collar mounted sawblades. The sawblades are operably mounted to the collars, and the collars in turn interface with the arbor through a set of keys and keyways. The keys and keyways interface with the arbor in an attempt to provide vertical support to prevent the sawblade from tilting and to maintain the blade in a direction perpendicular to the arbor. This patent suggests that the tolerances between the keyways and the support key arms are sufficient to allow lateral movement.
It has been found that such a system suffers from a variety of drawbacks and disadvantages. In practice, it has been found that collared sawblades cannot operate at the same high speeds as non-collared arbor driven blades. This is because the collars create a rigid boundary at the sides of the sawblade around the eye of the sawblade. Also, gaps exists between the blade and the collar. During a cutting operation, lateral side forces are inevitably transmitted to the sawblade and these lateral forces tend to cause the blade to flex. During flexing of the blade under side loading or during the subsequent restoration, the blade can impact the collar and rebound away from it. At sufficiently high speeds, this process or sequence of flexing and restoration can be aggravated by the blade-guide impact and rebounding. This can lead to sawblade instability and subsequent equipment damage.
Another disadvantage associated with the system disclosed in the aforementioned patent relates to the use of elongated key support arms. As noted, the key support arm and the collars are intended to maintain the blade perpendicular to the arbor. In practice, it has been found that significantly better operational performance of the sawblade can be obtained by allowing the blade to free float on the arbor and to adjust to the woodgrain pattern during cutting. This allows the sawblade to slightly tilt, and move back and forth (i.e., float) during cutting. In contrast, the presence of the elongated key support arms in the above-described system prevents the slight tilting of the sawblade. Instead, under lateral loading, the sawblade tends to flex out of its plane. Additionally, when subjected to side forces, by virtue of the elongated keys, the entire blade/collar system is not able to move along the arbor, or shift slightly back and forth, because the tight tolerances in the lever action at the ends of the elongated keys cause them to pinch the arbor. This can lead to undesirable jamming of the sawblade.